Automatic Twist and Sway Compensation in a Microwave Backhaul Transceiver

ABSTRACT

A first microwave backhaul transceiver may comprise an antenna array and circuitry. The circuitry may determine misalignment of the first microwave backhaul transceiver, and electronically adjust a radiation pattern of the antenna array to compensate for the determined misalignment of the microwave backhaul transceiver. The circuitry may perform the adjustment of the radiation pattern in real time to compensate for effects of wind on the microwave backhaul transceiver. The circuitry may detect movement of the microwave backhaul transceiver and translate the detected movement into angular misalignment of the radiation pattern of the antenna array. The adjustment of the radiation pattern of the antenna array may comprise an adjustment of a polarization orientation of the antenna array.

PRIORITY CLAIM

This application claims priority to and the benefit of the followingapplication(s), each of which is hereby incorporated herein byreference:

U.S. provisional patent application 61/809,935 titled “MicrowaveBackhaul” filed on Apr. 9, 2013;

U.S. provisional patent application 61/881,016 titled “MicrowaveBackhaul Methods and Systems” filed on Sep. 23, 2013; and

U.S. provisional patent application 61/884,765 titled “MicrowaveBackhaul Methods and Systems” filed on Sep. 23, 2013.

INCORPORATION BY REFERENCE

The entirety of each of the following applications is herebyincorporated herein by reference:

U.S. patent application Ser. No. 13/933,865 titled “Method And SystemFor Improved Cross Polarization Rejection And Tolerating CouplingBetween Satellite Signals” filed on Jul. 2, 2013.

BACKGROUND

Limitations and disadvantages of conventional approaches to microwavebackhaul will become apparent to one of skill in the art, throughcomparison of such approaches with some aspects of the present methodand system set forth in the remainder of this disclosure with referenceto the drawings.

BRIEF SUMMARY

Methods and systems are provided for automatic twist and swaycompensation in a microwave backhaul transceiver, substantially asillustrated by and/or described in connection with at least one of thefigures, as set forth more completely in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example microwave backhaul link between a firstmicrowave backhaul transceiver and a second microwave backhaultransceiver.

FIG. 2 shows an example implementation of a steerable microwave backhaultransceiver.

FIG. 3 shows an example implementation of the subassembly of FIG. 2.

FIG. 4A shows a first example implementation of the circuitry of FIG. 3.

FIG. 4B shows a second example implementation of the circuitry of FIG.3.

FIG. 5A shows an example configuration of the beamforming circuitry ofFIG. 4A.

FIG. 5B shows an example configuration of beamforming components of thedigital signal processing circuitry of FIG. 4B.

FIG. 6A illustrates effects of sway (e.g., due to wind) on a microwavebackhaul link between link partners.

FIG. 6B illustrates effects of twist (e.g., due to wind) on a microwavebackhaul link between link partners.

FIG. 6C illustrates effects of tower sway (e.g., due to wind) onpolarizations of a microwave backhaul link between link partners.

FIG. 7 is a flowchart illustrating an example process for misalignmentcompensation in a microwave backhaul transceiver.

DETAILED DESCRIPTION

As utilized herein the terms “circuits” and “circuitry” refer tophysical electronic components (i.e. hardware) and any software and/orfirmware (“code”) which may configure the hardware, be executed by thehardware, and or otherwise be associated with the hardware. As usedherein, for example, a particular processor and memory may comprise afirst “circuit” when executing a first one or more lines of code and maycomprise a second “circuit” when executing a second one or more lines ofcode. As utilized herein, “and/or” means any one or more of the items inthe list joined by “and/or”. As an example, “x and/or y” means anyelement of the three-element set {(x), (y), (x, y)}. As another example,“x, y, and/or z” means any element of the seven-element set {(x), (y),(z), (x, y), (x, z), (y, z), (x, y, z)}. As utilized herein, the terms“e.g.,” and “for example” set off lists of one or more non-limitingexamples, instances, or illustrations. As utilized herein, circuitry is“operable” to perform a function whenever the circuitry comprises thenecessary hardware and code (if any is necessary) to perform thefunction, regardless of whether performance of the function is disabled,or not enabled, by some user-configurable setting. As used herein,“microwave” frequencies range from approximately 300 MHz to 300 GHz and“millimeter wave” frequencies range from approximately 30 GHz to 300GHz. Thus, the “microwave” band includes the “millimeter wave” band.

FIG. 1 depicts an example microwave backhaul link between a firstmicrowave backhaul transceiver and a second microwave backhaultransceiver. Shown are a tower 108 to which access network antennas 112and remote radio head (RRH) 110 are attached, a baseband unit 104, atower 122 a to which microwave backhaul transceiver 120 a (comprisingsubassembly 114 a and reflector 116 a) is attached, and a tower 122 b towhich microwave backhaul transceiver 120 b (comprising subassembly 114 band reflector 116 b) is attached. At any particular time, there may beone or more active (i.e., carrying traffic or synchronized and ready tocarry traffic after a link setup time that is below a determinedthreshold) links 106 (shown as wireless, but may be wired or optical)between the RRH 110 and the BBU 104. At any particular time, there maybe one or more active backhaul links 118 between the pair of backhaultransceivers 120 a and 120 b and/or between one of the transceivers 120a and another one or more backhaul transceivers not shown.

The antennas 112 are configured for radiating and capturing signals ofan access network (e.g., 3G, 4G LTE, etc. signals to/from mobilehandsets). Although the example pair of microwave transceivers 120 a and120 b are used for backhauling cellular traffic, this is just oneexample type of traffic which may be backhauled by microwavetransceivers, such as 120 a and 120 b, that implement aspects of thisdisclosure.

For an uplink from a mobile handset to the core network 102, theantennas 112 receive signals from the handset and convey them to the RRH110. The RRH 110 processes (e.g., amplifies, downconverts, digitizes,filters, and/or the like) the signals received from the antennas 112 andtransmits the resulting signals (e.g., downconverted I/Q signals) to thebaseband unit (BBU) 104 via link(s) 106. The BBU 104 processes, asnecessary, (e.g., demodulates, packetizes, modulates, and/or the like)the signals received via link(s) 106 for conveyance to the microwavebackhaul transceiver 120 a via link 113 a (shown as wired or optical,but may be wireless). The microwave backhaul transceiver 120 aprocesses, as necessary (e.g., upconverts, filters, beamforms, and/orthe like), the signals from BBU 104 for transmission via the subassembly114 a and reflector 116 a over microwave backhaul link(s) 118. Themicrowave transceiver 120 b receives the microwave signals overmicrowave backhaul link(s) 118 via the subassembly 114 b and reflector116 b, processes the signals as necessary (e.g., downconverts, filters,beamforms, and/or the like) for conveyance to the cellular serviceprovider core network 102 via link 113 b.

For a downlink from the core network 102 to the mobile handset, datafrom the core network 102 is conveyed to microwave backhaul transceiver120 b via link 113 b. The transceiver 120 b processes, as necessary(e.g., upconverts, filters, beamforms, and/or the like), the signalsfrom the core network 102 for transmission via the subassembly 114 b andreflector 116 b over link(s) 118. Microwave transceiver 120 a receivesthe microwave signals over the microwave backhaul link(s) 118 via thesubassembly 114 a and reflector 116 a, and processes the signals asnecessary (e.g., downconverts, filters, beamforms, and/or the like) forconveyance to the BBU 104 via link 113 a. The BBU 104 processes thesignal from transceiver 120 a as necessary (e.g., demodulates,packetizes, modulates, and/or the like) for conveyance to RRH 110 vialink(s) 106. The RRH 110 processes, as necessary (e.g., upconverts,filters, amplifies, and/or the like), signals received via link 106 fortransmission via an antenna 112.

FIG. 2 shows an example implementation of a steerable microwave backhaultransceiver. The depicted transceiver 120 represents each of thetransceivers 120 a and 120 b described above with reference to FIG. 1.The example transceiver 120 comprises the subassembly 114 mounted to asupport structure 204 (which may, in turn, mount the assembly to themast/tower 122, building, or other structure, not shown in FIG. 2), anda link 113 which represents each of the links 113 a and 113 b. Thesubassembly 114 comprises an antenna array 202 which in turn comprises aplurality of antenna elements. The subassembly 114 may be mounted suchthat the antenna elements are positioned at or near a focal plane of thereflector 116. The subassembly 114 may comprise, for example, one ormore semiconductor dies (“chips”) arranged on one or more printedcircuit boards. The antenna elements may be, for example, horns and/ormicrostrip patches. In the example implementation depicted, the antennaelements capture signals reflected by reflector 116 for reception andbounce signals off the reflector 116 for transmission. The radiationpattern 208 of the antenna array 202 corresponds to a radiation pattern206 after reflection off the reflector 116. Although the radiationpatterns may comprise multiple lobes, only a main lobe is shown forsimplicity of illustration. In another implementation, the antennaelements may directly receive backhaul signals, or receive them througha lens, for example.

FIG. 3 shows an example implementation of the subassembly of FIG. 2. Theexample subassembly 114 comprises four feed horns 306 ₁-306 ₄, andcircuitry (e.g., a chip or chipset) 302. The circuitry 302 drivessignals to the horns 306 ₁-306 ₄ via one or more of feed lines 304 ₁-304₈ for transmission, and receives signals from the horns 306 ₁-306 ₄ viafeed lines 304 ₁-304 ₈ for reception. The circuitry 302 is operable tocontrol the phases and/or amplitudes of signals output to the feed lines304 ₁-304 ₈ so as to achieve desired transmit radiation patterns.Similarly, the circuitry 302 is operable to control the phases and/oramplitudes of signals received from the feed lines 304 ₁-304 ₈ so as toachieve desired receive radiation patterns.

The feed lines 304 ₁-304 ₄ correspond to a first polarization and thefeed lines 304 ₅-304 ₈ correspond to a second polarization. Accordingly,the subassembly 114 may be operable to concurrently receive twodifferent signals on the same frequency but having differentpolarizations, concurrently transmit two different signals on the samefrequency but having different polarizations, and/or concurrentlytransmit a first signal having a first polarization and receive a secondsignal having a second polarization. Furthermore, the radiation patternfor the two polarizations may be controlled independently of oneanother. That is two independent sets of amplitude and phase beamformingcoefficients may be maintained by circuitry 302 as, for example,described below with reference to FIGS. 5A-5B.

FIG. 4A show a first example implementation of the circuitry of FIG. 3.In the example implementation shown, the circuitry 302 comprises analogfront-ends 402 ₁-402 ₈, a beamforming circuit 404, analog-to-digitalconverter (ADC) 406, one or more sensors 414, digital circuitry 408, anda digital-to-analog converter (DAC) 440. The circuitry 302 outputsreceived data onto link 113 (e.g., coaxial cable) and receivesto-be-transmitted data via link 113.

The sensor(s) 114 may be operable to determine movement, orientation,geographic position, and/or other physical characteristics of thetransceiver 120. Accordingly, the sensor(s) 414 may comprise, forexample, a gyroscope, an accelerometer, a compass, a GPS receiver, alaser diode, a laser detector, and/or the like. Additionally oralternatively, the sensor(s) 114 may be operable to determineatmospheric conditions and/or other physical obstructions between thetransceiver 120 and potential microwave backhaul link partners (e.g.,the sensor(s) 114 may comprise, for example, a hygrometer, apsychrometer, and/or a radiometer). The sensor(s) 414 may outputreadings/measurements as signal 415.

For receive operations, each front-end circuit 402 _(n) (1≦n≦N, whereN=8 in the example implementation depicted) is operable to receive amicrowave signal via feed line 304 _(n). The front-end circuit 402 _(n)processes the signal on feed line 304 _(n) by, for example, amplifyingit via low noise amplifier LNA 420 _(n), filtering it via filter 426_(n), and/or downconverting it via mixer 424 _(n) to an intermediatefrequency or to baseband. The local oscillator signal 431 _(n) for thedownconverting may be generated by the circuit 404, as described below.The result of the processing performed by each front-end circuit 402_(n) is a signal 403 _(n).

The ADC 406 is operable to digitize signal 405 to generate signal 407.The bandwidth of the ADC 406 may be sufficient such that it canconcurrently digitize entire microwave backhaul bands comprising aplurality of channels or sub-bands (e.g., the ADC 406 may have abandwidth of 1 GHz or more).

The DAC 440 is operable to convert digital signal 439 (e.g., a digitalbaseband signal) to an analog signal 441.

For receive, the digital circuitry 408 is operable to process thedigital signals 407 for output to link 113. The processing may include,for example, symbol-to-bits demapping, FEC decoding, deinterleaving,equalizing, and/or the like. The processing may include, for example,performing an interference (e.g., cross-polarization interference)cancellation process such as is described in, for example, theabove-incorporated U.S. patent application Ser. No. 13/933,865. Theprocessing may include, for example, channelization to select, foroutput to the link 113, sub-bands or channels of the signal 407. Theprocessing may include, for example, band stacking, channel stacking,band translation, and/or channel translation to increase utilization ofthe available bandwidth on the link 113.

For transmit, the digital circuitry 408 is operable to perform digitalbaseband processing for preparing data received via link 113 to betransmitted via the microwave backhaul link(s) 118. Such processing mayinclude, for example, processing of packets received via the link 113 torecover the payload data from such packets, and then packetization,modulation, etc. to generate a microwave backhaul digital basebandsignal 439 carrying the payload data. Parameters used by the digitalcircuit 408 for processing the digital signals 407 may be adjusted basedon SNR and/or some other performance metric of the microwave backhaullink(s) 118. Thus, rather than having fixed parameters (packet size,bandwidth, modulation order, FEC code word length, and/or the like)designed to handle worst-case conditions, microwave backhaultransceivers in accordance with this disclosure may be operable to takeadvantage of the fact that most of the time worst-case conditions arenot present and, therefore, parameters may be adjusted to increaserange, increase throughput, decrease latency, decrease powerconsumption, and/or the like during non-worst-case conditions.

The beamforming circuit 404 comprises local oscillator synthesizer 428operable to generate a reference local oscillator signal 429, andcomprises phase shift circuits 430 ₁-430 _(N) operable to generate Nphase shifted versions of signal 429, which are output as signals 431₁-431 _(N). The amount of phase shift introduced by each of the circuits430 ₁-430 _(N) may be determined by a corresponding one of a pluralityphase coefficients. The plurality of phase coefficients may becontrolled to achieve a desired radiation pattern of the antennaelements 306 ₁-306 ₄ (e.g., to compensate for misalignment as describedwith reference to FIGS. 6A-7 below). In another example implementation,additional front-end circuits 402 and phase shifters 430 may be presentto enable concurrent reception of additional signals via the antennaelements 306 ₁-306 _(N).

The beamforming circuit 404 also comprises a circuit 432 which isoperable to perform weighting of the signals 403 ₁-403 ₈ by theirrespective amplitude coefficients determined for the desired radiationpattern (e.g., to compensate for misalignment as described withreference to FIGS. 6A-7 below). For reception, the circuit 432 isoperable to combine the weighted signals prior to outputting them onsignal 405.

In an example implementation, the phase and/or amplitude coefficientsmay be controlled/provided by the digital circuitry 408 via signal 416.The phase and amplitude coefficients may be adjusted dynamically. Thatis, the coefficients may be adjusted while maintaining one or moreactive backhaul links. For example, the phase and amplitude coefficientsmay be adjusted in real time to compensate for twist and sway as it isoccurring.

In an example implementation, the phase and/or amplitude beamformingcoefficients may be controlled based on data retrieved from a localand/or networked database. Such data may include, for example, dataindicating geographical locations of one or more other microwavebackhaul transceivers with which the transceiver 120 may desire toestablish a microwave backhaul link. Such data may, for example, be usedin combination with the transceiver's own location for determining adirection and distance to the other transceiver.

The implementation of circuitry 302 shown in FIG. 4A may be realized onany combination of one or more semiconductor (e.g., Silicon, GaAs) diesand/or one or more printed circuit board. For example, each front-endcircuit 402 _(n) may comprise one or more first semiconductor dieslocated as close as possible to (e.g., a few centimeters from) itsrespective antenna element 306 _(N), the circuits 404 and 406 maycomprise one or more second semiconductor dies on the same PCB as thefirst die(s), the circuits 408 and 440 may reside on one or more thirdsemiconductor dies on the same PCB, and the sensor(s) 414 may bediscrete components connected to the PCB via wires or wirelessly.

FIG. 4B depicts a second example implementation of the circuitry 302. Inthis example implementation, the application of beamforming amplitudeand phase coefficients is performed in the digital domain in digitalcircuitry 408. That is, in addition to other functions performed bydigital circuitry 408 (such as those described above), the digitalcircuitry may also perform phase and amplitude weighting and combiningof the signals 413 ₁-413 ₈.

Each of the circuits 450 ₁-450 ₈ is operable to performdigital-to-analog conversion (when used for transmission) and/oranalog-to-digital conversion (when used for reception). In this regard,for reception, the signals 413 ₁-413 ₈ are the result of digitization ofthe signals 403 ₁-403 ₈ output by the front-ends 402 ₁-402 ₈. Fortransmission, the signals 413 ₁-413 ₈ are the result of digitalcircuitry 408 performing phase and amplitude weighting and combining ofone or more digital baseband signals (the weighting and combining may beas described in FIG. 5B, for example).

The implementation of circuitry 302 shown in FIG. 4B may be realized onany combination of one or more semiconductor (e.g., Silicon, GaAs) diesand/or one or more printed circuit board. For example, each pair of 402_(n) and 450 _(n) may comprise an instance of a first semiconductor dieand may be located as close as possible to (e.g., a few centimetersfrom) its respect antenna element 306 _(n), the digital circuitry 408may comprise an instance of a second semiconductor die on the same PCBas the first dies, and the sensor(s) 414 may be discrete componentsconnected to the PCB via wires or wirelessly.

Referring now to FIG. 5A, there is shown an example implementation ofthe circuit 232 that supports spatial routing of a full-duplex microwavebackhaul link. In the example implementation shown, the signals 403₁-403 ₄ correspond to a received signal having a first polarization(e.g., horizontal) and the signals 403 ₅-403 ₈ correspond to a signal tobe transmitted with a second polarization (e.g., vertical).

In the receive direction, each of the signals 403 ₁-403 ₄ has beenreceived via a respective one of antenna elements 306 ₁-306 ₄, and hadits phase shifted, during downconversion by a respective one of mixers402 ₁-402 ₄, by a respective phase coefficient of a selected first setof coefficients. In circuit 232, the amplitude of each of signals 403₁-403 ₄ is scaled by a respective amplitude coefficient of the selectedfirst set of coefficients. The weighted signals are summed resulting insignal 405. The signal 405 thus corresponds to a received signal using aradiation pattern corresponding to the selected first set of phase andamplitude coefficients.

In the transmit direction, the signal 441 is split into four signals,each of which has its amplitude scaled by a respective amplitudecoefficient of a selected second set of coefficients. The result of theamplitude scaling is signals 403 ₅-403 ₈. The signals 403 ₅-403 ₈ areconveyed to front-ends 402 ₅-402 ₈ where, during upconversion tomicrowave frequency, each is phase shifted by a respective phasecoefficient of the selected second set of coefficients. The upconvertedsignals are then conveyed, via feed lines 304 ₅-304 ₈, to antennaelements 306 ₁-306 ₄ for transmission.

For both transmitting and receiving with the same link partner on thesame frequency, the first set of phase and amplitude coefficients is thesame as second set of phase and amplitude coefficients. This may beachieved by storing a single set of coefficients and providing the sameset to both scaling circuits 502 ₁-502 ₄ and 502 ₅-502 ₈.

For transmitting to a first link partner while receiving from a secondlink partner on the same frequency, the first set of phase and amplitudecoefficients is the different than the second set of phase and amplitudecoefficients. This may be achieved by storing two sets of coefficientsand providing the first set to circuits 502 ₁-502 ₄ and the second setto circuits 502 ₅-502 ₈. This enables independently adjusting the twosets of coefficients which corresponds to independently steering thetransmit and receive radiation patterns (e.g., for steering the transmitradiation pattern to track misalignment with a first link partner towhich the transceiver transmits and for steering the radiation patternto track misalignment with a second link partner from which thetransceiver receives).

Referring now to FIG. 5B, there is shown an example implementationdigital circuitry that supports spatial routing of a full-duplexmicrowave backhaul link. In the example implementation shown, thesignals 413 ₁-413 ₄ correspond to a received signal having a firstpolarization (e.g., horizontal) and the signals 413 ₅-413 ₈ correspondto a signal to be transmitted with a second polarization (e.g.,vertical).

In the receive direction, each of the signals 413 ₁-413 ₄ has beenreceived via a respective one of antenna elements 306 ₁-306 ₄,downconverted by a respective one of mixers 402 ₁-402 ₄, and digitizedby a respective one of circuits 450 ₁-4504. The circuits 504 ₁-504 ₄scale the amplitudes of the signals 403 ₁-403 ₄ by respective amplitudecoefficients of a selected first set of coefficients. The circuits 504₁-504 ₄ also phase shift the signals 403 ₁-403 ₄ by respective phasecoefficients of the selected first set of coefficients. The resultingphase-shifted and amplitude-scaled signals are then combined to generatesignal 508. The signal 508 thus corresponds to a received signal using aradiation pattern corresponding to the selected first set of phase andamplitude coefficients.

In the transmit direction, the signal 510 is split into four signals.Each of the circuits 504 ₅-504 ₈ scales a respective one of the signal413 ₅-413 ₈ by a respective amplitude coefficient of a selected secondset of coefficients. Each of the circuits 504 ₅-504 ₈ shifts a phase ofa respective one of the signal 413 ₅-413 ₈ by a respective phasecoefficient of the selected second set of coefficients. The result ofthe amplitude scaling is signals 403 ₅-403 ₈. The signals 403 ₅-403 ₈are conveyed to circuits 450 ₅-450 ₈ where they are converted to analogsignals 403 ₅-403 ₈. The signals 403 ₅-403 ₈ are then upconverted byfront-ends 402 ₅-402 ₈ and then conveyed, via feed lines 304 ₅-304 ₈, toantenna elements 306 ₁-306 ₄ for transmission.

For both transmitting and receiving with the same link partner on thesame frequency, the first set of phase and amplitude coefficients may bethe same as second set of phase and amplitude coefficients. This may beachieved by storing a single set of coefficients and providing the sameset to both scaling circuits 504 ₁-504 ₄ and 504 ₅-504 ₈.

For transmitting to a first link partner while receiving from a secondlink partner on the same frequency, the first set of phase and amplitudecoefficients may be different than the second set of phase and amplitudecoefficients. This may be achieved by storing two sets of coefficientsand providing the first set to circuits 504 ₁-504 ₄ and the second setto circuits 504 ₅-504 ₈. This enables independently adjusting the twosets of coefficients which corresponds to independently steering thetransmit and receive radiation patterns (e.g., for steering the transmitradiation pattern to track misalignment with a first link partner towhich the transceiver transmits and for steering the radiation patternto track misalignment with a second link partner from which thetransceiver receives).

Although the example implementations in FIGS. 5A and 5B use differentpolarizations to enable concurrent transmission and reception on thesame frequencies, other implementations may use different frequenciesfor transmit and receive (where the antenna elements 306 ₁-306 ₄ aresufficiently broadband to cover the different frequencies). In suchimplementations, different sets of coefficients for transmit and receivemay be needed to achieve transmit and receive radiation patterns havingsubstantially similar directivity.

FIG. 6A illustrates effects of tower sway (e.g., due to wind) on amicrowave backhaul link between link partners. For reference, acoordinate system comprising angles θ and φ is shown, with the angle θsweeping along the plane of the page and θ sweeping perpendicular to thepage. Shown are the transceivers 120 a and 120 b mounted to towers 122 aand 122 b, respectively. The towers 122 a and 122 b and transceivers 120a and 120 b in their nominal positions are shown by solid lines andresult in beams 602 and 604. The sway in the negative θ direction, andthe resulting beams 602 ^(−θ) and 604 ^(−θ), are shown by dashed lines.Sway in the positive θ direction, and the resulting beams 602 ^(+θ) and604 ^(+θ), are shown by dotted lines. The amount of angular deflectionof beam 602 between its nominal position and its position shown as 602^(−θ) is indicated by arc 606. The amount of angular deflection of beam602 between its nominal position and its position shown as 602 ^(+θ) isindicated by arc 608. The amount of angular deflection of beam 604between its nominal position and its position shown as 604 ^(−θ) isindicated by arc 612. The amount of angular deflection of beam 604between its nominal position and its position shown as 604 ^(+θ) isindicated by arc 610. In an example implementation, an angulardeflection of 1.7° could result in 10 dB of loss for a two meterdiameter dish communicating in a frequency band centered around 18 GHz.

In an example implementation, the materials, dimensions, etc., of thetowers 122 a and 122 b and transceivers 120 a and 120 b may be chosenbased on a maximum amount of sway that is to be tolerated under maximumwind conditions that are to be tolerated (e.g., designed to sway lessthan 1.7° in winds of 60 mph or less). Similarly, given the knownmaximum angular deviation, the transceivers 120 a and 120 b may bedesigned to be capable of compensating for the maximum angulardeviations. For example, the number and size of antenna elements 306 andthe size of reflectors 116 may be selected for each of the transceivers120 a and 120 b such that the transceivers 120 a and 120 b are capableof sufficiently steering their respective radiation patterns to maintainat least a threshold SNR (and/or some other metric) even when both beams602 and 604 are at a maximum deflection (in the +θ direction, forexample).

FIG. 6B illustrates effects of tower twist (e.g., due to wind) on amicrowave backhaul link between link partners. For reference, acoordinate system comprising angles θ and φ is shown, with the angle φsweeping along the plane of the page and θ sweeping perpendicular to thepage. Shown are the transceivers 120 a and 120 b mounted to towers 122 aand 122 b, respectively. The transceivers 120 a and 120 b in theirnominal positions are shown by solid lines and result in beams 602 and604. Twist in the negative φ direction, and the resulting beams 602^(−φ) and 604 ^(−φ), are shown by dashed lines. Twist in the positive φdirection, and the resulting beams 602 ^(+φ) and 604 ^(+φ), are shown bydotted lines. The amount of angular deflection of beam 602 between itsnominal position and its position shown as 602 ^(−φ) is indicated by arc614. The amount of angular deflection of beam 602 between its nominalposition and its position shown as 602 ^(+φ) is indicated by arc 616.The amount of angular deflection of beam 604 between its nominalposition and its position shown as 604 ^(−φ) is indicated by arc 620.The amount of angular deflection of beam 604 between its nominalposition and its position shown as 604 ^(+φ) is indicated by arc 618. Inan example implementation, an angular deflection of 1.7° could result in10 dB of loss for a two meter diameter dish communicating in a frequencyband centered around 18 GHz.

In an example implementation, the materials, dimensions, etc. of thetowers 122 a and 122 b and transceivers 120 a and 120 b may be chosenbased on a maximum amount of twist that is to be tolerated under maximumwind conditions that are to be tolerated (e.g., designed to twist lessthan 1.7° in winds of 60 mph or less). Similarly, given the knownmaximum angular deviation, the transceivers 120 a and 120 b may bedesigned to be capable of compensating for the maximum angulardeviations. For example, the number and size of antenna elements 306 andthe size of reflectors 116 may be selected for each of the transceivers120 a and 120 b such that the transceivers 120 a and 120 b are capableof sufficiently steering their respective radiation patterns to maintainat least a threshold SNR (and/or some other metric) even when both beams602 and 604 are at a maximum deflection (in the +φ direction, forexample).

FIG. 6C illustrates effects of tower sway (e.g., due to wind) onpolarization orientation of a microwave backhaul link between linkpartners. For reference, a coordinate system comprising angle γ isshown, with the angle γ sweeping along the plane of the page. Shown arethe transceivers 120 a and 120 b mounted to towers 122 a and 122 b,respectively.

The tower 122 a and transceiver 120 a (comprising 116 a and 114 a) inits nominal positions is shown by solid lines. The nominal horizontalpolarization for transceiver 120 a is shown as solid line 656, and thenominal vertical polarization for transceiver 120 a is shown as solidline 654. Sway of the tower 122 a and transceiver 120 a in the positiveγ direction is shown as dashed lines (with 122 a ^(+γ), 116 a ^(+γ), and114 a ^(+γ) called out) results in horizontal polarization 656 ^(+γ) andvertical polarization 654 ^(+γ). Sway of the tower 122 a and transceiver120 a in the negative γ is shown as dotted lines (with 122 a ^(−γ), 116a ^(−γ), and 114 a ^(−γ) called out) and results in horizontalpolarization 656 ^(−γ) and vertical polarization 654 ^(−γ). Absentaspects of this disclosure, the angular deviation of the polarizationorientations may result in increased cross-polarization interferencebetween a signal being transmitted or received on the verticalpolarization and a signal being transmitted or received on thehorizontal polarization. In an exemplary implementation, however, thetransceivers 120 a may be operable to determine the angular deviation ofthe polarization orientations and adjust the radiation patterns based onthe determined angular deviation and/or implement a cross-polarizationinterference cancellation process that adapts based on the determinedangular deviation.

The tower 122 b and transceiver 120 b (comprising 116 b and 114 b) inits nominal positions is shown by solid lines. The nominal horizontalpolarization for transceiver 120 a is shown as solid line 652, and thenominal vertical polarization for transceiver 120 a is shown as solidline 650. Sway of the tower 122 b and transceiver 120 b in the positiveγ direction is shown as dashed lines (with 122 b ^(+γ), 116 b ^(+γ), and114 b ^(+γ) called out) and results in horizontal polarization 652 ^(+γ)and vertical polarization 650 ^(+γ). Sway of the tower 122 b andtransceiver 120 b in the negative γ is shown as dotted lines (with 122 b^(−γ), 116 b ^(−γ), and 114 b ^(−γ) called out) and results inhorizontal polarization 652 ^(−γ) and vertical polarization 650 ^(−γ).In an exemplary implementation, however, the transceiver 120 b may beoperable to determine the angular deviation of the polarizationorientations and adjust the radiation patterns based on the determinedangular deviation and/or implement a cross-polarization interferencecancellation process that adapts based on the determined angulardeviation.

FIG. 7 is a flowchart illustrating an example process for misalignmentcompensation in a microwave backhaul transceiver. The process beginswith block 702.

In block 702, the microwave backhaul transceiver 120 a is installed onmast 122 a. Installation may comprise initial alignment of thetransceiver 120 a within determined tolerances. The initial alignmentmay, for example, be based on readings of the sensors 414 and/orinstruments (levels, compasses, etc.) in use by the installationtechnician. The initial alignment may, for example, be based on one ormore signals to and/or from one or more intended link partners of thetransceiver 120 a (e.g., to and/or from transceiver 120 b). Such signalsmay be, for example, signals specifically generated for alignment (e.g.,four signals for monopulse tracking in azimuth and elevation).

The installation may comprise calibrating the sensor(s) 414. Forexample, after initial alignment, readings form sensor(s) 414 may bemonitored over a period of time and then averaged (to compensate forwind, vibrations, etc. during installation) to determine sensor readingsthat correspond to the initial alignment. The initial alignment mayresult in an initial set of beamforming coefficients and initialparameters used by the cross-polarization interface cancellation processperformed by digital circuitry 408.

In block 704, one or more active microwave backhaul links 118 areestablished between transceiver 120 a and link partner 120 b. The linkmay be established using the nominal radiation pattern(s) andcross-polarization interference cancellation parameters determined inblock 704. In an example implementation, the transceivers 120 a and 120b may initially use signaling parameters that enable successfullyestablishing the link(s) 118 even in the presence of poorsignal-to-noise ratio (e.g., due to residual misalignment within thetolerances of the initial alignment). Then, after the SNR improves(e.g., as a result of alignment compensation performed in blocks 706 and708) the signaling parameters may be changed to improve the performance(e.g., measured in terms of throughput, reliability, and/or the like) ofthe link(s) 118.

In block 706, the transceiver 120 a determines its own absolutemisalignment, absolute misalignment of its link partner(s), and/ormisalignment relative to its link partner(s).

In an example implementation, the transceiver 120 a may determine itsown absolute misalignment based on, for example, readings output by itssensor(s) 414. Deviations of the sensor readings from the nominal sensorreadings determined in block 702 may be interpreted as movement of thetransceiver 120 a. The digital circuitry 408 may then translate thedeviations of the sensor readings to angular deflection of directivityand/or polarization orientation of the radiation pattern(s) of thetransceiver 120 a. The determined angular deflection may then be used bydigital circuitry 408 to adjust the beamforming coefficients and/oradjust parameters used by the cross-polarization interference process.

In an example implementation, the transceiver 120 a may determine itsown absolute misalignment based on, for example, monopulse tracking of afixed target (e.g., a target on a building). The digital circuitry 408may translate the reflections of the monopulse tracking signals toangular deflection of directivity and/or polarization orientation of theradiation pattern(s) of the transceiver 120 a. The angular deflection ofantenna directivity and/or polarization orientation may then be used bydigital circuitry 408 to adjust the beamforming coefficients and/oradjust parameters used by the cross-polarization interference process.

In an example implementation, the transceiver 120 a may determinerelative misalignment between it and one or more link partners based on,for example, monopulse tracking of the link partner(s). The digitalcircuitry 408 may translate the reflections of the monopulse trackingsignals to relative angular deflection of directivity and/orpolarization orientation between the radiation patterns of thetransceivers 120 a and 120 b. The relative angular deflection may thenbe used by digital circuitry 408 to adjust the beamforming coefficientsand/or adjust parameters used by cross-polarization interferenceprocess.

In an example implementation, the transceiver 120 a may determinerelative misalignment between it and one or more link partners based on,for example, an amount of cross-polarization interference measured bythe digital circuitry 408. For example, an average amount ofcross-polarization interference over a time interval of determinedlength may be at a minimum for optimal alignment and may increase asrelative rotational angular deviation increases.

In an example implementation, the transceiver 120 a may determineabsolute misalignment of its link partner(s) based on absolutemisalignment data (e.g., raw sensor readings, raw monopulse signalreflection levels, values of measured performance metrics, and/orangular deviation in radians or degrees) received from the linkpartner(s) via the backhaul link(s) 118 (e.g., sent via the backhaullink(s) 118 on a high-reliability control channel that ensures deliveryeven with very low SNR) and/or via an alternate link (e.g., via alow-latency, low-bandwidth wired link, optical fiber link, and/orwireless link operating at a cellular frequency or otherlower-than-microwave frequency that is not as dependent online-of-sight.) In this regard, the link partner(s) may determine theirown misalignment and send the determined misalignment to transceiver 120a. Similarly, the transceiver 120 a may send its determined misalignmentto its link partner(s).

In an example implementation, where each link partner knows its ownmisalignment, each may attempt to adjust its radiation pattern(s) and/orcross-polarization interference cancellation parameters to compensatefor its own misalignment. In another example implementation, where oneor both of the link partners only knows relative misalignment, one ormore protocols may be implemented to prevent over-compensation. As anexample, each link partner may attempt to compensate for only half ofthe relative misalignment. As another example, it may be predetermined(e.g., during link establishment in block 702) that a particular one ofthe link partners will attempt to compensate for relative misalignmentup to a threshold and the other link partner will attempt to compensateonly for relative misalignment above the threshold. As another example,it may be predetermined (e.g., during link establishment in block 702)that a particular one of the link partners will attempt to compensateonly for certain types of misalignment (e.g., directional orpolarization orientation) and the other link partner will attempt tocompensate only for other types of misalignment. As another example, thelink partners may coordinate compensation through real-time datadelivered over a control channel of the link 118 and/or over analternate link.

In block 708, the digital circuitry 408 of the transceiver 120 aattempts to compensate for the misalignment determined in block 706.

In an example implementation, where the misalignment is directional, thedigital circuitry 408 may adjust beamforming coefficients to steer theradiation pattern in the opposite direction of the misalignment (e.g.,if the misalignment is in the +θ and −φ directions, the beamformingcoefficients may be adjusted to steer the radiation pattern in the −θand +φ directions).

In an example implementation, where the misalignment is rotational, thedigital circuitry 408 may adjust beamforming coefficients to rotate thepolarization orientation of its radiation pattern in the oppositedirection of the misalignment (e.g., if the misalignment is in the +γdirection, the beamforming coefficients may be adjusted to rotate thepolarization orientation in the −γ).

In an example implementation, where the misalignment is rotational, thedigital circuitry 408 may adjust parameters used by thecross-polarization interference cancellation process.

In accordance with an example implementation of this disclosure, a firstmicrowave backhaul transceiver (e.g., 120 a) may comprises an antennaarray (e.g., 202) and circuitry (e.g., 302). The circuitry is operableto determine misalignment of the first microwave backhaul transceiver,and electronically adjust a radiation pattern of the antenna array tocompensate for the determined misalignment of the microwave backhaultransceiver. The circuitry may be operable to perform the adjustment ofthe radiation pattern in real time to compensate for effects of wind onthe microwave backhaul transceiver. The circuitry may be operable todetect movement of the microwave backhaul transceiver, and translate thedetected movement into angular misalignment of the radiation pattern ofthe antenna array. The circuitry may comprise one or both of: anaccelerometer and a gyroscope, and may be operable to perform thedetection of the movement based on readings from one or both of theaccelerometer and the gyroscope. The adjustment of the radiation patternof the antenna array may comprise an adjustment of a polarizationorientation (e.g., measured as an angle γ in FIG. 6C) of the antennaarray. The circuitry may be operable to perform monopulse tracking forthe determination of the misalignment. The circuitry may be operable toconcurrently receive a first signal having a first polarization and asecond signal having a second polarization. The circuitry may beoperable to perform a cross-polarization interference cancellationprocess for mitigating the impact of interference between the firstsignal and the second signal. The circuitry may be operable to adjustparameters used by the cross-polarization interference cancellationprocess based on the detected misalignment of the first microwavebackhaul transceiver. The circuitry may be operable to concurrentlytransmit a first signal having a first polarization and receive a secondsignal having a second polarization. The circuitry may be operable toperform a cross-polarization interference cancellation process formitigating the impact of interference between the first signal and thesecond signal. The circuitry may be operable to adjust parameters usedby the cross-polarization interference cancellation process based on thedetected misalignment of the first microwave backhaul transceiver. Thecircuitry may be operable to establish a microwave backhaul link with asecond microwave backhaul transceiver. The circuitry may be operable toreceive, from the second microwave backhaul transceiver, data indicatingmisalignment of the second microwave backhaul transceiver, and adjustthe radiation pattern of the antenna array based on the data. Thecircuitry may be operable to track a position of the second microwavebackhaul transceiver using monopulse tracking, and adjust the radiationpattern of the antenna array based on the tracked position of the secondmicrowave backhaul transceiver.

The present method and/or system may be realized in hardware, software,or a combination of hardware and software. The present methods and/orsystems may be realized in a centralized fashion in at least onecomputing system, or in a distributed fashion where different elementsare spread across several interconnected computing systems. Any kind ofcomputing system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computing system with a program orother code that, when being loaded and executed, controls the computingsystem such that it carries out the methods described herein. Anothertypical implementation may comprise an application specific integratedcircuit or chip. Some implementations may comprise a non-transitorymachine-readable (e.g., computer readable) medium (e.g., FLASH drive,optical disk, magnetic storage disk, or the like) having stored thereonone or more lines of code executable by a machine, thereby causing themachine to perform processes as described herein.

While the present method and/or system has been described with referenceto certain implementations, it will be understood by those skilled inthe art that various changes may be made and equivalents may besubstituted without departing from the scope of the present methodand/or system. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the presentdisclosure without departing from its scope. Therefore, it is intendedthat the present method and/or system not be limited to the particularimplementations disclosed, but that the present method and/or systemwill include all implementations falling within the scope of theappended claims.

What is claimed is:
 1. A system comprising: a first microwave backhaultransceiver that comprises an antenna array and circuitry operable to:determine misalignment of said first microwave backhaul transceiver; andelectronically adjust a radiation pattern of said antenna array tocompensate for said determined misalignment of said microwave backhaultransceiver.
 2. The system of claim 1, wherein said circuitry isoperable to perform said adjustment of said radiation pattern in realtime to compensate for effects of wind on said microwave backhaultransceiver.
 3. The system of claim 1, wherein said circuitry isoperable to: detect movement of said microwave backhaul transceiver; andtranslate said detected movement into angular misalignment of saidradiation pattern of said antenna array.
 4. The system of claim 3,wherein: said circuitry comprises one or both of: an accelerometer and agyroscope; said circuitry is operable to perform said detection of saidmovement based on readings from one or both of said accelerometer andsaid gyroscope.
 5. The system of claim 1, wherein said adjustment ofsaid radiation pattern of said antenna array comprises an adjustment ofa polarization orientation of said antenna array.
 6. The system of claim1, wherein said circuitry is operable to perform monopulse tracking forsaid determination of said misalignment.
 7. The system of claim 1,wherein said circuitry is operable to: concurrently receive a firstsignal having a first polarization and a second signal having a secondpolarization; perform a cross-polarization interference cancellationprocess for mitigating the impact of interference between said firstsignal and said second signal; adjust parameters used by saidcross-polarization interference cancellation process based on saiddetected misalignment of said first microwave backhaul transceiver. 8.The system of claim 1, wherein said circuitry is operable to:concurrently transmit a first signal having a first polarization andreceive a second signal having a second polarization; perform across-polarization interference cancellation process for mitigating theimpact of interference between said first signal and said second signal;adjust parameters used by said cross-polarization interferencecancellation process based on said detected misalignment of said firstmicrowave backhaul transceiver.
 9. The system of claim 1, wherein saidcircuitry is operable to: establish a microwave backhaul link with asecond microwave backhaul transceiver; receive, from said secondmicrowave backhaul transceiver, data indicating misalignment of saidsecond microwave backhaul transceiver; and adjust said radiation patternof said antenna array based on said data.
 10. The system of claim 1,wherein said circuitry is operable to: establish a microwave backhaullink with a second microwave backhaul transceiver; track a position ofsaid second microwave backhaul transceiver using monopulse tracking; andadjust said radiation pattern of said antenna array based on saidtracked position of said second microwave backhaul transceiver.
 11. Amethod comprising: in a first microwave backhaul transceiver thatcomprises an antenna array: determining misalignment of said firstmicrowave backhaul transceiver; and adjusting a radiation pattern ofsaid antenna array to compensate for said determined misalignment ofsaid microwave backhaul transceiver.
 12. The method of claim 11,comprising adjusting said radiation pattern in real time to compensatefor effects of wind on said microwave backhaul transceiver.
 13. Themethod of claim 11, comprising: detecting movement of said microwavebackhaul transceiver; and translating said detected movement intoangular misalignment of said radiation pattern of said antenna array.14. The method of claim 13, comprising detecting said movement based onreadings from one or both of an accelerometer and a gyroscope of saidfirst microwave backhaul transceiver.
 15. The method of claim 11,wherein said adjusting of said radiation pattern of said antenna arraycomprises adjusting a polarization orientation of said antenna array.16. The method of claim 1, comprising performing monopulse tracking forsaid determining of said misalignment.
 17. The method of claim 1,comprising: concurrently receiving a first signal having a firstpolarization and a second signal having a second polarization;performing a cross-polarization interference cancellation process formitigating the impact of interference between said first signal and saidsecond signal; adjusting parameters used by said cross-polarizationinterference cancellation process based on said detected misalignment ofsaid first microwave backhaul transceiver.
 18. The method of claim 11,comprising: concurrently transmitting a first signal having a firstpolarization and receive a second signal having a second polarization;performing a cross-polarization interference cancellation process formitigating the impact of interference between said first signal and saidsecond signal; adjusting parameters use by said cross-polarizationinterference cancellation process based on said detected misalignment ofsaid first microwave backhaul transceiver.
 19. The method of claim 1,comprising: establishing a microwave backhaul link with a secondmicrowave backhaul transceiver; receiving, from said second microwavebackhaul transceiver, data indicating misalignment of said secondmicrowave backhaul transceiver; and adjusting said radiation pattern ofsaid antenna array based on said data.
 20. The method of claim 11,comprising: establishing a microwave backhaul link with a secondmicrowave backhaul transceiver; tracking a position of said secondmicrowave backhaul transceiver using monopulse tracking; and adjustingsaid radiation pattern of said antenna array based on said trackedposition of said second microwave backhaul transceiver.